Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.30   6.281%   $232.0114   $232.01   $232.00   $232.00  
  Purchase #2 $203.97   6.220%   $216.6569   $216.66   $216.65   $216.70  
  Purchase #3 $52.60   7.464%   $56.5261   $56.53   $56.55   $56.50  
  Purchase #4 $46.50   9.149%   $50.7543   $50.75   $50.75   $50.80  
  Purchase #5 $247.66   13.286%   $280.5641   $280.56   $280.55   $280.60  
  Purchase #6 $228.81   5.399%   $241.1635   $241.16   $241.15   $241.20  
  Purchase #7 $173.91   8.775%   $189.1706   $189.17   $189.15   $189.20  
  7 purchase totals = $1,171.75       $1,266.8469   $1,266.84   $1,266.80   $1,267.00